The present invention relates to improvements in RADIOACTIVE WASTE DISPOSAL, and more particularly to the disposal of radioactive materials by immobilizing them within a solid mass for storage and/or burial.
It is well known that waste products occur as a natural result of activity involving the use of radioactive isotopes. For example, waste products are provided during the operation of atomic reactors and the like, and these waste products may be produced directly from primary radiation sources or secondarily by the creation of isotopes from non-radioactive metals or the like. In order to assure smooth efficient continuation of atomic processes generating such waste material, efficient disposal means must be provided both for primary and secondary waste products.
At the present time, disposal has been achieved by immobilizing the waste in a solid block, and then by disposal at sea or by burial in a specially designated burial site. Burial at sea requires more and more preparation, because of the long range effects of certain pollution components that might build up. When the product is disposed of at a burial site, it is also necessary to provide safe means for transporting the material to the burial site. In addition, it is important to assure the containment and safe storage of the material at the burial site for a time sufficient to allow a sufficient decay of the radioactive components to reduce the radiation intensity thereof to a relatively safe level. Thus it is seen that whatever the disposal of the waste material, it is important to provide means for protecting the material and assuring its safe storage at the disposal site for a long period of time.
Prior to this invention, Portland Cement has been in rather widespread use for the purpose of encapsulating and holding radioactive waste material therewithin so as to provide a protective block for the material at the burial site. Portland cement has been found to be particularly advantageous where the radioactive waste material is present in water, and it is advantageous to dispose of a certain amount of water along with the radioactive waste material in order to provide an efficient handling process.
For example, the water utilized in the cooling loop of atomic reactors tends to accumulate contaminations of radioactive nickel and cobalt probably as a result of conversion of iron and/or nickel in the tubes carrying the water. In any event, these materials build up in the water so that it is important to remove the waste from time to time in order to prevent a buildup from reaching a very hot or hazardous level. In such a case, probably the most serious component is cobalt 60, because it emits hard gamma rays and has a half-life of approximately five years.
Prior to this invention, the cooling water was removed and mixed with Portland Cement in the usual water-cement ratio, allowed to solidify and then the block of cement buried in a waste dump. Such disposal has been generally satisfactory for many operations, but it has a number of disadvantages. One of the disadvantages resides in the heavy weight of the cement and the like, which must be transported often over a considerable distance. Another disadvantage, and perhaps a more serious one, resides in the fact that many waste products of this general class now contain levels of boron material that render disposal in Portland Cement unsatisfactory or impossible because of the lack of compatability of the materials. Other areas of improvement are also seen to be available, such as the handling problems occuring with cement in processing equipment and the possibility of the cement setting up in an undesired fashion during an unexpected shutdown. Rather than go into all of the disadvantages of the cement process, it is proposed to provide an improved process in which certain advantages are achieved, and which is particularly suitable for disposing of waste products having high concentrations of compounds containing boron.
Another problem which has been of some concern with the use of Portland Cement is the possibility of the radioactive material leaching therefrom. This problem is particularly acute where disposal at sea is contemplated, and efforts to utilize materials other than Portland Cement have generally been in the area of the use of hydrophobic materials so as to render the solid block substantially leach-proof. However, the use of hydrophobic materials such as bitumen or asphalt has a number of disadvantages particularly in the mixing and processing steps, and the use of these materials has generally been rejected as not substantially improving the situation involved with the use of Portland Cement.